1. Field of the Invention
The present invention relates to a two-stage fuel injector equipping the combustion chambers of gas turbines.
2. Discussion of the Background
It improves devices such as that described in French patent 2 832 492, the structure and operation of which can be summarized as follows. Two valves are arranged in series in an outer bushing of the injector and are biased separately into closed positions by respective springs. The fuel fed into the injector by a pump passes through a filter and weighs on the first valve, which is a primary valve biased by a weak spring. A moderate pressure is therefore enough to open said valve, and the fuel passes through it and then flows along a primary path which leads it out of the injector. The primary path comprises an annular portion between the outer bushing and an inner body, in which the other valve or secondary valve is housed in a sliding manner. The fuel also weighs on the secondary valve, which is biased by a much stronger spring than the previous spring. It therefore does not move until a pressure is reached which is greater than that necessary to displace the primary valve and to open the primary fuel path, but once it too has been opened it opens up a secondary fuel path which branches from the primary fuel path and passes through the secondary valve. The flow of fuel delivered by the injector is then increased by the additional flow which flows through this secondary fuel path. This secondary flow is used in certain regimes of the engine in which the injector is employed.
The idea here is to enrich the mixture delivered by the injector, i.e. to increase the fuel flow, but only in the primary flow regime. This enrichment might be required in order to improve the ignition capacity during high-altitude flight and also on the ground. It will concern only some of the injectors of the engine. The temptation will therefore be to modify existing injectors instead of using a completely new design or a different model. It will in particular be advantageous if the injector sought is identical to the existing injector with regard to the parts governing the secondary flow.